==IRSE & Railway Signalling > Railway Signalling

Principle of SACEM in MTRC:
Like the topic of ATP, SACEM is a ATP system which operate as Distance-to-go mode. It's mainly operate by the trackside computer system communicate to carry out the train position and distance to the forward train, here's the operating principle of SACEM.

Thereˇs two methods to transmit information for the computer to the train though the track, continuously transmit and intermissive transmit. And for the train to the computer, it's use semi-continuously transmit.

Intermissive transmit:
Beacons: mainly use for identify the train position, there are, Relocation Beacons(RB), Stationary Train Initialization beacons(STIB) and Moving Train Initialization Beacons(MTIB).

The RB is the normal one, it mainly install in the main line, it's use for identify the position of a moving train, it's operate by the induce current induced by the beacon sensor of the train and the coil of the beacon, this induce current include the address code of the beacon to let the train identify the position of the moving train by checking the (MAP) in the computer of the train, it's because of the self-induce current property, so RB is no need for connect to the power supply.

Relocation Beacon:
Initialization process: when the SACEM just operate, it can't identify the train position, so it's necessary to let the beacon for setting the train computer, and this is initialization process. Here are two kinds of beacon specially for this purpose.

STIB is mainly install in the depot exit, terminal or U-turn track. When the train leave the depot, it use for identify the train position to the train computer, it's different between RB because of when the train leave the depot, itˇs at stationary, so can't induce electric field to induce current, and that's why STIB need to connect to the power supply.

Another kind of beacon for initialization process is MTIB. It's mainly install in the main line, when the train delocalise, it use to reset the train computer call relocalise. So MTIB mainly install in the place where easily to get delocalise. MTIB is combine by two normal beacons, it's operate by the fixed distance of two beacons to let the train computer to re-calculate and identify the train position, furthermore, it's same as RB, it no need for connect to the power supply.

Continuous transmit and semi-continuous transmit:
Loops: In fact, it is the electric wire where located beside the track to transmit and receive electric signal so as to let the computer of the control room communicate with the computer in the train. Loops basically divided two kinds, Return Channel Loop, Continuous Transmission Loop. Return Channel Loop install in the platform area, it is used to receive the information of train status which transmit by the train computer when the train stop in the station, this is call semi-continuous transmit; Continuous Transmission Loop is located in the block area for transmitting the light signal, status of the track circuit, track (map) to the train computer, this is call continuous transmit. On the other hand, AEL is using Injection Loop, what so special is that it is use to transmit electric signal though the track to the train computer by using the coil in the track between some interval.

The electric signal equipment in the train:
In both train head and tail, it have install the equipment of transmit and receive electric signal, they are Continuous Transmission Antenna and Beacon Sensor, Continuous Transmission Antenna is use for receive the electric signal from the Continuous Transmission Loop; Beacon Sensor is use for receive electric signal from beacon and transmit signal back to Return Channel Loop.

Sector Computer:
The computer which locate along the line, use to process the signal, interlocking and the communication between other control system, also, transmit the status of track circuit and other information to the train computer though the Loops. At the same time, the sector computer will transmit that track interval (map) to the train computer though the Loops to let the ATP system arrange the information of the beacon and forward train distance to calculate the braking distance.

The control of SACEM-----Train's cab:
In every cab of people carried train, it have mode selector, it totally have four kinds of mode for the train operator to choose: they are AM (Auto Mode), CM (Coded Manual), RM (Restrict Manual), FB (Fallback). When the train in AM mode, train operator just push START button to Start the ATO system, to let the train brake and control the speed automatically base on the ATP system, then there is no need to manual when train moving. When ATO system not function well, train operator need to change to CM mode, the principle of CM mode is similar to ATP, train operator follow the Cab signal to manually operate the train, when the speed apart to the Target speed of 3km/h left, the alarm inside the cab will warn the operator, when the speed over the Target speed, emergency braking system will automatically switch on. And RM is use when the SACEM system delocalise and in the depot, when operating in RM mode, the train are not control by ATP, so the Max. safe speed is 22km/h, the operator need to control the train manually, also there is no any cab signal appoint, the alarm will warming when the speed reach at 19km/h. FB mode is similar to RM mode, but when operating in FB mode, the SACEM system in the train tail will switch on, so the operator can reversing train. The FB mode basically will not use in main line, it just for operate in depot and once the computer hardware breakdown. Also, if the operator wants to use RM or FB mode, he should permit by the control center.

The control of SACEM-----OCC:
Inside the OCC (Operation Control Center) of AEL and every SCR (Station Control Room) have a ATSS (Automatic Train Supervisory System) which use to control the SACEM and Interlocking system though SMT (Station Maintenance Terminal) in every station. ATSS mainly combine of two parts: ATS (Automatic Train Supervision), it is use for monitor and input of some parameter and it can be manually set the route. ATR (Automatic Train Regulation): It can automatically set the route and astrict the speed in specific interval. Inside the OCC, It have two ATSS of every single line, each one control half of the line operation, it is control by the TC (Traffic Controller), TC will input the train schedule into the ATSS before operating the railway system everyday.